2.4E rebuild update!

[dtw]

I managed to get my major engine components to Carolina Speedwerkes for appraisal by David Brown. Verdict: Crank looks great, rod bearings are in spec (both ends), heads are clean, exhaust valve guides are shot, cylinders are clean but one obviously requiring replacement, rods in good shape, case overall looking good. The main bearing bores are out of round by .002", but can be bored out to the maximum extent of the "standard" bearing tolerance (no oversize or special bearings required). Here's the work we're going to do:

-Install new valve guides & springs, and valves as necessary
-Flow heads approximately 7-8 cfm
-Round up main bearing bores in case
-Install time certs in trans stud holes. (my engine was previously helicoiled and actually pulled the coils and fell off the engine stand during disassembly, narrowly missing my feet...grrrrr)
-Hot-tank & magnaflux case
-Replace damaged cylinder
-Micropolish & clean crankshaft
-Recondition rods

I suffer from "while we're in here" syndrome, unfortunately. The E cams will soon be sent out for an S grind, and I've sourced some Webers to use until I have the kilodollars necessary to properly redo the MFI. I'm dissatisfied with the prospects of replacing my 1 damaged piston, or finding 6 used 2.2 pistons to raise compression a bit. I've decided to simply buy a new set of JE pistons. My questions are these
-what would be the maximum recommended compression for a street & track engine running pump gas? And yes, I'd like to retain the 2.4L displacement so I don't have to go into serious head and case machining. I've heard JE pistons run up to half a point high on CR?

-Any suggestions other than the "S" grind?

[dtw]

-bump-

[gaijinda]

Bump again. (Good questions).

[J P Stein]

I put 9.7:1 Shasta Pistons in my 2.7L. I did some light prep work on the piston tops to eliminate sharp/thin edges. Premimum pump gas seems to do the trick for street and AX work.

Having said that, detonation could be occuring and I might not be able to hear it. This is right on the edge for a single plug motor, me thinks. Only time will tell if it is a step too far.

If I track it, I will use racing gas.

[Early_S_Man]

Dave,

How about the JE 85 mm oversize pistons that EBS now advertises? You could get you Biral cylinders bored and honed to final size AFTER getting the JE's ... for optimum clearance. I think 9.5:1 would be the maximum you should plan for ... considering the declining quality of pump gas!

GE-60 cams are an alternative to 'S' that Matt Holcomb seems to like pretty well!

[jluetjen]

-Flow heads approximately 7-8 cfm

Could you help and translate this into an intake port diameter? How deep inside the ports did you have to port? BTW - do you know what the diameter of the intake ports was to start with?

The 2.4E's were right on the ragged edge of Porsche's intake gas speed (about 100 meters/second) so porting seems to be the right thing to do. If you are going to run anything wilder then the stock E-cam's it would seem to be a requirement. I agree that the GE60's seem to be comparable to the S cams, but a little less peaky. The Webcam 104/102 is also comparable, but a touch wilder.

If you happen to dyno the engine afterwords, it would be interesting to see the results. It might also give you some confidence regarding setting the timing without melting the pistons.

[zotman72]

I would get an SC oil pump and do the oil bypass mod as well. You will need an SC oil screen to go with it. Teflon coat your new rod and main bearings (EBS did this for me). Rebush your rods and balance them within spec (< 6 grams I think). Raceware rod bolts (you were not considering reusing your originals were you?).
Remove the windage screens and new intermediate shaft bearings. Update chain sprockets and new ramps/chains.
You might make sure all your intake and exhaust ports are the same size, if not even them up with a Dremel. I have seen several sets of heads having a range of port varying sizes.

[dtw]

Warren-
Will the 2.5 (math?) pistons require the same case and head work that a 2.7 conversion would require? 9.5 is around what I figured for max CR. At 1 point above the S spec 2.4, that should be a heck of a fun motor, especially with a few other tweeks.

Jluetjen- Don't know how far he's going with depth or diameter of porting- he's not done with 'em yet! But the base diameter is 32mm on both sides. For comparison, the S ran 36mm.

The GE60 is looking attractive- I'm interested in keeping the peaky characteristics in check.

Zotman- No plans to reuse rod bolts! ..though not sure if Raceware will be used..maybe.. Nor was I especially thrilled about the idea of putting those windage trays back in. Rods will be reconditioned and balanced. Why an SC pump and oil bypass mod? Thanks for the replies so far...

[jluetjen]

Remove the windage screens...

Why? Even in a dry sump motor, windage trays help to pull the oil out of the air in the crank case which does make a difference for HP. Did you ever notice that it is harder pedalling a bike in the rain? The same deal applies to oil. Every time the crank hits a droplet of oil in the gallary, it adds drag to the crank. You won't notice this a lower rev's, but it will sap HP at higher RPM's where S cam will be giving you peak HP.

DTW; the reason I asked about the existing port diameter is because Warren recently checked a 2.4T (MFI) head and the intake ports were about 29 mm's in diameter. That is quite a bit smaller then the 32 mm's that I was expecting. For comparison, I was curious if your heads actually were 32 mm or something else. As far as the 36 mm ports on the S head, if that is the diameter which you are going to use, that should be fine for any motor from stock 2.4E up to about 225 horse power. I was curious if you were going to use a different diameter or just the standard S size.

I've been collecting a lot of data about port size, cam selection and the ensuing results. I've got some calculations which I think will do a pretty reasonable job of predicting the HP and Torque charactoristics. For fun I'd like to test them on your car. Here's what I'm guesstimating for two of the configurations which are being discussed here.

* Baseline 1: Stock 2.4E, 8.0 to 1 CR. 32 mm ports. 165 HP at 6200 RPM, 151 lb/ft at 4500 RPM.

* Baseline 2: Stock 2.4S, 8.5 to 1 CR. 36 mm ports. 190 HP at 6500 RPM, 158 lb/ft at 5200 RPM.

* Configuration 1 - "Long Stroke 2.5": 85 mm pistons, 9.5:1 CR. 2.5 liters, 36 mm ports, 'S' cam. 85 meters/second intake gas speed. >>>199 HP at 6500 RPM, 168 lb/ft at 5200 RPM. <<<
* Configuration 2 - "Long Stroke 2.5 w/ GE60 Cam. 9.5:1 CR, 2.5 liters, 36 mm ports. 83 meters/second intake gas speed. >>> 193 HP at 6300 RPM, 168 lb/ft at 5100 RPM. <<<

The rub is that by advancing or retarding the cam timing, you might move the RPM numbers up or down by a couple of hundred RPM. Either version sounds like it will be a lot of fun.

[zotman72]

On the windage trays, I agonized on this last year. I talked to several 911 engine builders for racers here in the Denver area and they were all recommending leaving them out. This was a subjective call on my part. What does BA recommend? I am curious as to whether these trays even exist in the later motors.

One other tip on the engine, boatailing your case. It is supposedly good for reducing internal air resistance/turbulence and a couple hp. I did mine by hand with emory cloth., magnesium is soft and quite easy to smooth out.

Oh and the SC pump provides more pump capacity on the engine pressure side and is aluminium rather that magnesium. Again, this upgrade was recommended to me by folks I trusted. If you put the two types of pump side by side you can see the difference. Another thing, do check the internals of oil pump, especially the SCs if they have stored dry. The steel gears can create galvanic corrosion on the aluminium case, this I discovered when I bought one and the seller admonished me if I opened up I bought it. Sure as heck, I opened it as everything going into my 2.4S engine was going be inspected and it was totally corroded! I did get my money back. Finding good used SC oil pumps is not easy either, but my oil pressure is excellent.
HTH

[dtw]

John-
From the way David @ Speedwerkes was talking, it didn't sound as though he had any specific port size in mind; more like he would open and smooth the ports until he achieved a desired CFM rate. Now you have me curious, though- I'll measure the port size when I get the heads back and let you know.

Your calculations/estimates are in line with my seat-of-the-pants feelings on the motor- 200 hp or just shy of it with these modifications. In a lightweight early chassis, that's going to be a whole lot of fun.

Zot-
Cool deal about the pump. I'll keep an eye out for one. For that matter, would a good used 964 pump work just as well? Those seem to be the pumps of choice for high-performance rebuild guys around here. As far as boattailing goes, we looked at the webs on my mag case, they appear to be rather well rounded right out of the box. David didn't feel there would be any appreciable gain from further work on them, so we're going to leave them alone. I'll ask him about the windage screens!

So 9.5 appears to be the consensus on max CR for street gas. What about the stroker motor Warren proposes? Questions:
-Case and head work go along with that?
-Does this prompt the timecerted head studs? While I'm still playing with only 2.4L, David is recommending I leave the studs alone.

Thanks,
Dave

[Wayne 962]

If you're not going to install case-savers (not timecerts) in your case, then you're asking for trouble.

Also the oil pump bypass mod is basically a requirement while you're in there.

Also, you can have your case resized to std/std by Competition Engineering - don't settle for a bore-out that will destroy your case for future rebuilds.

Cases aren't typically magnafluxed, who suggested that?

If your main bearing bores are out of round, then chances are the spigot surfaces are not level either. You need to have these machined flat or the engine will leak when put back together...

JE can basically make any piston you want, so you pick the CR. 9.5:1 is good for street and pump gas...

Are you planning on doing a valve job, or just replacing your valves & springs. That would be bad...

???

-Wayne

[dtw]

Nope, complete valve job. Valves will only be replaced if necessary.

Sorry, no magnafluxing on case, that was the crank.

Bypass mod- I'll ask about that, and the spigots too.

Case-savers- are you talking about shuffle pinning? He didn't think it necessary at 200hp but I'll check again.

-d

[Early_S_Man]

Dave,

Actually, the 85 mm pistons would only get you up to a 'true' 2.4, or 2397 cc, and the more I think about it ... at around $1000 for the JE's and boring and honing your old cylinders ... FORGET about THAT SUGGESTION!

I really think the RS 2.7 p & c are a better deal at $1350 from EBS! And, the machining of the case and heads is not that much if you are having all of the work done at once by CE, or any other competent shop! I think you would be a LOT happier with a RS 2.7 clone engine than just a 'happy' 2.4! Think real hard about 225 hp!!!

Wayne was talking about case inserts (sometimes called case savers) for the 24 head studs ... not shuffle pinning. And ... it is just too easy and logical to do it at this time, rather than cut corners and hope for the best! Yes, the 964 is a great pump, but so is a Carrera or SC pump ... for a street engine, and the oil bypass mod is a no-brainer with the engine apart!

[jluetjen]

...more like he would open and smooth the ports until he achieved a desired CFM rate.

I didn't mean to sound like I'm doubting your builder. My question was because it is very difficult to map a CFM rate to what you see in an engine. Also, the CFM will vary depending on the vacuam applied, so 20 CFM at X inches of mercury will not map to 20 CFM at Y inches of mercury.

In my opinion, CFM is very important when you're dealing with American V8's with square ports. Why? Because the port size is limited by water jackets and push rods. Square ports do not also do not flow as well as round ports because of the increased surface area and dead air near the corners. Also very often the ports are not straight, but have a bend in them which biases the air flow in one direction or another. Given those constraints, shape is everything. There may be two 1.5 x 2 inch ports that have completely different flow charactoristics, and one will flow better then the other. CFM numbers will help to differentiate between the two.

With 911's, a lot of that does not apply. There are no water jackets or push rods. The initial shape is basically straight and circular. What can you do with that? Basically you can make them bigger or not. I have determined that the S heads gradually open up by 5 mm's near the boss for the valve guide - I suspect to keep the cross-sectional area consistant and avoid constricting the flow. I have not yet been able to examine some T/E heads closely, but as I mentioned, so far I've learned that they are different. In general, my theory (and I'm welcome to opposing view points and data) is that as long as the ports are not too small (causing an intake gas speed above 100 m/s at the peak HP engine speed) or too large (causing the intake gas speed at peak torque to drop below 51 meters/second) you're OK. 36 mm ports like the stock S heads will fufill the above requirement. If your builder goes with something different, I'd be interested is learning the affects (if any)

Since you are doing this in your engine right now, it seemed like a good opportunity to collect some more data. You know what they say - "Inquiring minds want to know!". Especially since this has so much to do with an engine's performance and most people treat it as a "black art".

[dtw]

Wow...good stuff, good stuff!!!

John- nope, I didn't think you were doubting my engine builder. He's a good guy and I trust him- I've seen some of the engines he's built!

Warren...what can I say? You're absolutely killing me. Twisting indian burns into my virtual arm. I hear the exhaust note now. Next time I talk to the shop...I'll see how much is involved in prepping the heads and case for 2.7 goodies. Where does EBS get their cylinders from? Are they Mahles? American Air Cooled? Alright, alright, I'll ask around...the car and engine aren't going to be done for quite some time anyway, I can always spring for the 2.7 gear later.

Ah, so you mean timecerting the head studs...well, if I jump to 2.7, it is a no brainer. If I stay at 2.4...all those who have advised so far, the balance leans at leave 'em as is.

Hehehehe, I knew you guys were going to do this to me. Love it.

-Dave

[zotman72]

Wayne is right on with Competition Engineering. They worked on my 5R case, case savers(do it no question), oil bypass and decked the case so I could use standard bearings. I had a dirty Carrera oil cooler wreak havoc on my oil passages so I had CE pull the plugs and clean out all the passages. I can not say enough about the quality of their work. You do usually have a 8-12 week return cycle with him as Walt is the best in biz. That EBS price on 2.7 P/Cs, is that for a MFI set or CIS?
As to the later oil pumps, well they have different pickups with a snorkel like attachment, the sump plate screen stops with the SCs. I think the SC pump was the one for me because of that pickup change.